Fiber reinforced plastic pipe has come into reasonably extensive use in recent years for handling corrosive materials, petrochemicals and the like where metallic pipe is unsuitable. Glass fiber reinforcements are employed so that pipe can withstand appreciable pressures. Epoxy resins are often used and a thin lining layer of epoxy or other material is commonly used for enhancing resistance to chemicals. The pipes are formed by winding rovings of glass fiber coated with epoxy resin in helical paths around a cylindrical mandrel and curing the resin. Such pipes can be made economically and it is desirable to make economical fittings for such pipes, such as tees, crosses, laterals or Y's, elbows and reducers.
Techniques have been developed for economically winding pipe elbows which are essentially sharply curved sections of pipe having two ends. Economical techniques have not been developed for winding pipe tees, crosses, and laterals since they have much more complicated geometry. Unlike an elbow having two ends, a pipe tee has three ends. This greatly complicates the winding problems since it is important to cover all areas of the tee with a sufficient thickness of fibers with proper orientation for resisting the complex stress distributions in a tee without excess thickness being built up in other areas.
A variety of machines have been proposed for winding fiber reinforced plastic pipe tees and the like. These machines have been limited in the patterns of windings that can be made because of limitations on the motions available by the pipe fitting or roving delivery system. Such machines are slow and require a substantial time to wind a pipe fitting, thereby significantly increasing cost, both because of poor utilization of the machine and the increased labor required for attending the machine. Such machines have been devoted to a single purpose such as winding a tee rather than being universally useful for a variety of pipe fittings.
A variety of winding patterns have been developed which collectively can cover a pipe tee with fibers in suitable orientations. A variety of patterns for winding such a pipe tee are described in U.S. patent application Ser. No. 186,338 filed Sept. 11, 1980, by Ralph S. Friedrich and Kenneth Charles Naylor, and in U.S. patent application Ser. No. 186,335 filed Sept. 11, 1980, by Ralph S. Friedrich and Ronald G. Ulrich. Both of these applications are assigned to the same assignee as this application. The subject matter of these applications is hereby incorporated by reference.
Such patterns can be wound by hand but the resultant pipe tee would be expensive. It is therefore desirable to provide apparatus for winding a fiber reinforced pipe tee or other pipe fitting rapidly and reproducibly. Since a variety of winding patterns are needed, it is preferable that such a machine be controlled electronically, that is with the so-called "numerical control" systems now available. Readily available electronic systems will synchronously control three axes, that is, three directions of motion, either angular or linear, at the same time. Although four axis controllers are also commercially available, the increased complexity and smaller production of such numerical control systems makes them appreciably most costly. Many so-called four axis numerical control systems actually control only three axes simultaneously and the fourth axis is time shared electrically with one of the others. For winding a pipe tee, such systems can require complicated hardware. It is therefore desirable to provide a machine for winding pipe fittings where three axes of numerical control are sufficient. Developing a program or sequence of control functions for a four axis numerical control system is notably more complex than developing a program for three axes. There is no advantage to a more costly and complex control system when a three axis system can be used to produce the same results.